A fortiori argument

An a fortiori argument /ˈɑː fɔːrtɪˈoʊriː/ is an "argument from a yet stronger reason." The phrase a fortiori is Latin for "from [something] stronger".

An a fortiori argument draws upon existing confidence in a proposition to argue in favor of a second proposition that is held to be implicit in the first. The second proposition may be considered "weaker," and therefore the arguer adduces a "stronger" proposition to support it.